THE PHYSIOPATHOLOGY OF EPILEPTIC SEIZURES 



357 



which an occipital EEG discharge accompanying a 

 visual episode follows or precedes a temporal dis- 

 charge with aphasia (60, 76). 



The second eventuality explains the fact that any 

 partial seizure may become generalized. Generaliza- 

 tion takes place more readily when the partial seizure 

 is more intense, when it occupies a ree;ion closely con- 

 nected to the centrencephalic reticular formation, 

 and when the patient has an epileptic predisposition 

 or, in other words, generalized neuronal hyperexcita- 

 bilitx'. When all these conditions are present, the 

 partial seizure becomes generalized almost immedi- 

 ately, and the localizing signs at the onset may pass 

 unobserved. One must therefore always question the 

 patient and eye witnesses closely on the mode of onset 

 of ' generalized' seizures, and carry out an EEG exam- 

 ination, even when the diagnosis .seems indisputable, 

 for a large number of seizures apparentK generalized 

 from the start are found to be partial epilepsy second- 

 arily generalized. 



The evolution of partial discharges originating on 

 the spot (primary discharges) depends upon the same 

 factors of fatigue as in generalized discharges and 

 perhaps also on the same phenomena of rhythmical 

 inhibition. For this reason their EEG arrangement is 

 usually the same as in generalized discharges. Rhyth- 

 mic activity is first sustained in the saine way at the 

 initial frequency (indefatigability), then slowed pro- 

 gressively (growing fatigability), and finalK' inter- 

 rupted by episodes of silence or slow waves which 

 grow progressively longer (phase of exhaustion or in- 

 hibition), until at the end there is silence (phase of 

 postictal extinction). 



On the other hand, partial discharges remote from 

 the epileptogenic lesion develop completely differ- 

 ently, in a way which defies all classification because 

 of seizure variability. These discharges are char- 

 acterized by slow sinusoidal or notched waves, or by 

 polyphasic spikes with an initial positive phase, and 

 they are notable for their long duration and their in- 

 stability. At one moment a discharge may be rhyth- 

 mical and of large amplitude and at the next it has 

 lost these features. The discharge may be slowed or 

 accelerated indifferently and sometimes even pass 

 through two or three successive phases of speeding up 

 and slowing down. Finally, there may or may not be 

 postictal extinction, and in some cases the record be- 

 comes normal again immediately after the discharge 

 has ended. 



DISTINCTION BETWEEN TWO GREAT V.^RIETIES OF PAR- 

 TIAL EPILEPSY WITH RESPECT TO CHARACTER OF THEIR 



DiscH.\RGES. The \arious partial epilepsies have often 

 been classified according to the structures in which the 

 seizure develops, or at least in which it originates. 

 Such a conception obviously presupposes that the dis- 

 charge always originates in the same place, that it is 

 always propagated along the same pathways and that 

 it always provokes the same electroclinical signs. It 

 also presuppo.ses that the first symptom, the 'signal- 

 symptom' or 'aura' is the same every time, points in- 

 fallibly to the site of the lesion and guides the hand of 

 the neurosurgeon. 



Such rules, however, apply only to a small minority 

 of the partial epilepsies, namely those provoked by a 

 very limited irritative lesion whose discharge involves 

 a closed neuronal system. In the majority of cases, 

 however, these rules are only partially applicable, par- 

 ticularly when the epileptogenic lesion is extensive 

 and when the discharge dev'elops in complex neuronal 

 systems where it is propagated irregularly and differ- 

 ently in various seizures and accordingly provokes 

 complex and variable symptoms. In such ca.ses, the 

 'signal-symptom' is clearly less valuable (54, 76, 79), 

 for it may reveal a discharge propagated from a 

 clinically silent structure and it may \ary from one 

 seizure to another according to the origin and propa- 

 gation of the discharge. 



Two varieties of partial epilepsy are distinguished 

 in the Marseille school (59), according to propagation 

 of the discharge to different anatomical systems. 



a) In the first variety, the causal discharge orig- 

 inates in a structure essentially, if not exclusively, 

 connected to one single other structure. Together 

 they constitute a limited functional system, the two 

 ' poles' (these two structures) being united by dense 

 fibers. In this system, the discharge extends from one 

 pole to the other but always stays limited within the 

 system, for although other fibers unite each pole to 

 other nervous formations, they are never grouped 

 sufficiently densely to cause effective bombardment 

 and to render these other formations epileptic. The 

 most notable examples of these ' bipolar' systems in the 

 brain are the corticothalamic sectors connecting the 

 various specific areas of the cortex to the correspond- 

 ing specific thalamic nuclei (54). 



The EEG manifestations consist exclusively of dis- 

 charges limited to the sector concerned and, in con- 

 sequence, are recorded from a very localized region 

 of the scalp. The interseizure discharges consist of 

 sporadic spikes or spikes-and-waves which, in current 

 EEG usage, reveal an 'epileptogenic focus'; the 

 seizure discharges are spikes repeated rhythmically 



